PLATINUM-INDUCED MORPHOLOGY AND REACTIVITY CHANGES ON W(111)

The structure and CO chemisorption properties of a model bimetallic sy stem Pt on W(111) have been studied using Auger electron spectroscopy (AES), low energy electron diffraction (LEED), scanning tunneling micr oscopy (STM), and thermal desorption spectroscopy (TDS). The results r eveal that upon annealing, the Pt/W(111) system undergoes a variety of structural transformations, with the most striking being the reconstr uction of the W(111) substrate to form pyramidal facets with {211} ori entations. The presence or absence of facets, and size distribution of the facets, are sensitive functions of Pt coverage and annealing temp erature. LEED results for faceted surfaces annealed to different tempe ratures correlate well with the STM data. CO has been used as a probe molecule to examine the chemisorption properties of the different stru ctural phases. Increasing Pt coverage causes site blocking that result s in reduced dissociative adsorption of CO.